A spokesman for Pakistan's army says authorities have forced an Indian military helicopter to land and have taken its four-member crew into custody for violating Pakistani airspace.

Major-General Athar Abbas said the incident occurred at about 1:00pm (08:00 GMT) on Sunday in Olding-Kargil sector near Skardu, a city in northeastern Pakistan fairly close to the border with India-administered Kashmir.

"The helicopter had came deep into our airspace. It was forced to land. Four Indian army officers have been taken into safe custody. They are safe," Abbas told the Reuters news agency. The four include three pilots and one crew chief, the Associated Press reported.

"According to the spokesman for the Pakistani military ... this particular helicopter penetrated across the line of control which divides the two armies, then it went almost 25 km into Pakistani airspace, and that is when the military told this helicopter to land," reported Al Jazeera's Kamal Hyder from Islamabad, the Pakistani capital.

"Even though there were suggestions that it may have been bad weather, it appears that this was a deep penetration. What the Pakistanis now want to find out is was this a reconnaissance mission, was it carrying out some sort of an operation inside Pakistani lines or was this indeed an accident."

Abbas did not say what Pakistan planned to do with them, but said India had been informed and "investigations are under way".

"The helicopter was warned. The Indians would have realised that they were quite deep inside Pakistani airspace, so it landed without any incident we are told," reported Hyder.

"This is unprecedented because both sides have put their forces on the ground - the Indians have deployed troops on their border, so incidents like these unlikely to happen ... they don't happen all the time."

The Associated Press news agency reported that the helicopter was a Lama model that had been modified for high-altitude flight.

The last violation of Pakistani airspace by Indian aircraft occured shortly after the 2008 Mumbai attacks, when two Indian warplanes "inadvertently" incurred into Pakistani airspace at two different locations on December 14, 2008.

Pakistan and India have fought three major wars since they gained independence from Britain in 1947.